Method of handling a damage information-assisted hybrid ARQ scheme and related communication device

ABSTRACT

A method of handling a retransmission of a hybrid automatic repeat request scheme for a receiver in a communication system is disclosed. The method comprises receiving a first payload from a transmitter in the communication system, and feeding back a resource index to the transmitter, to indicate a size for a second payload in the next reception, when the receiver is unsuccessful to decode the first payload into a plurality of information bits, wherein the transmitter encodes the plurality of information bits into the first payload by using an error correction code.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/357,113, filed on Jun. 22, 2010 and entitled “Methods and Apparatusfor Damage Information-assisted Hybrid ARQ Scheme”, the contents ofwhich are incorporated herein in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method used in a communication systemand related communication device, and more particularly, to a method ofhandling a damage information-assisted hybrid ARQ scheme in acommunication system and related communication device.

2. Description of the Prior Art

An automatic repeat request (ARQ) scheme is used between a transmitterand a receiver in a communication system to provide reliable datatransmission. For example, when the ARQ scheme is used, a packet istransmitted with redundant bits generated by an error detection code(EDC) (e.g. a cyclic redundancy check (CRC) code) by the transmitter tothe receiver. After the receiver receives the packet with the redundantbits, the receiver checks correctness of the packet by using the EDC. Ifthe packet is received without any error, the receiver feedbacks anacknowledgment (ACK) to inform the transmitter that the packet has beenreceived correctly. After the transmitter receives the ACK, thetransmitter can continue to transmit successive packets. Oppositely, ifthe packet is received with an error, the receiver feedbacks a negativeacknowledgment (NACK) to inform the transmitter that the packet has notbeen received correctly. After the transmitter receives the NACK, thetransmitter retransmits the packet until an ACK is received.

However, the reliable data transmission using the ACK scheme isinefficient. For example, there is a great opportunity that the packetis received with small errors (e.g. a small number of error bits) and itis not necessary to retransmit the whole packet such that resources oftime, frequency and/or code are wasted. In this situation, if an errorcorrection code (ECC) (e.g. a convolutional code) is used, the packetcan easily be corrected and the resources are saved. Therefore, a numberof feeding back the NACK and retransmission can be reduced. A hybridautomatic repeat request (HARQ) scheme is proposed based on thisconcept.

The HARQ scheme is used in the communication system to provide bothefficient and reliable data transmissions. Different from the ARQscheme, both the EDC and the ECC are used in the HARQ scheme. Forexample, when the HARQ scheme is used, the transmitter encodes thepacket into a payload by using the EDC and the ECC, and transmits thepayload to the receiver. After the receiver receives the payload, thereceiver decodes the payload into a decoded packet by using the ECC andchecks the decoded packet by using the EDC. If the decoded packet iscorrect without any error, the receiver feedbacks an ACK to inform thetransmitter that the packet has been received correctly. Oppositely, ifthere is an error with the decoded packet, the receiver feedbacks theNACK to the transmitter. Since the packet with the small errors can becorrectly decoded by using the ECC without feeding back the NACK, i.e.,requesting a retransmission, throughput of the communication system isincreased due to fewer retransmissions.

Furthermore, there are three types of the HARQ scheme: type-I, type-IIand type-III schemes. In the type-I HARQ scheme, a receiver decodes anewly retransmitted payload and discards the payloads of the previousreceptions. Therefore, information in the payload of the previoustransmission is not exploited, and performance loss is caused. In thetype-II and type-III HARQ schemes, the receiver combines the newlyretransmitted payload and the payloads of the previous receptions toperform a joint decoding. Therefore, comparing with the type-I HARQscheme, performances of the type-II and type-III HARQ schemes areimproved due to a combination of the payloads. Besides, there are twomethods for performing the combination: chase combining (CC) andincremental redundancy (IR). When using the chase combining, the samepayload is transmitted in a retransmission. When using the incrementalredundancy, a different part of the payload with a fixed size istransmitted in the retransmission. It has been shown that performance ofthe incremental redundancy is better than performance of the chasecombining.

However, the performance of the incremental redundancy is limited due tothe fixed size of the retransmitted payload. In detail, an amount oferrors in the decoded packet is different in each retransmission.Accordingly, amounts of redundant bits and information of the packetrequired in the retransmitted payload for the receiver to perform thejoint decoding successfully are also different. In this situation, thefixed size of the retransmitted payload may be excessive or insufficientfor accommodating the amounts of redundant bits and information of thepacket. Not only the resources may be wasted when the fixed size is toolarge, but more retransmissions may be needed when the fixed size is toosmall. Therefore, there is a room to improve the performance byadjusting the size of the retransmitted payload in each retransmission.How to adjust the size of the retransmitted payload in eachretransmission of the HARQ scheme including the type-II or the type-IIIsuch that a better performance is achieved is a topic for discussion.

SUMMARY OF THE INVENTION

The disclosure therefore provides a method and related communicationdevice for handling a damage information-assisted HARQ scheme to solvethe abovementioned problems.

A method of handling a retransmission of a hybrid automatic repeatrequest (HARQ) scheme for a receiver in a communication system isdisclosed. The method comprises receiving a first payload from atransmitter in the communication system, and feeding back a resourceindex to the transmitter, to indicate a size for a second payload in thenext reception, when the receiver is unsuccessful to decode the firstpayload into a plurality of information bits, wherein the transmitterencodes the plurality of information bits into the first payload byusing an error correction code (ECC).

A method of handling a retransmission of a hybrid automatic repeatrequest (HARQ) scheme for a transmitter in a communication system isdisclosed. The method comprises receiving a resource index from areceiver, wherein the resource index indicates a size for a payload,encoding a plurality of information bits into the payload with the sizeby using an error correction code (ECC), and transmitting the payload tothe receiver in the communication system.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an exemplary communication systemaccording to the present invention.

FIG. 2 is a schematic diagram of an exemplary communication deviceaccording to the present invention.

FIG. 3 is a flowchart of an exemplary process according to the presentinvention.

FIG. 4 is a schematic diagram of a transmitter and receivercommunicating with each other according to an example of the presentinvention.

FIG. 5 is a flowchart of an exemplary process for generating the damageinformation according to an example of the present invention.

DETAILED DESCRIPTION

Please refer to FIG. 1, which is a schematic diagram of a communicationsystem 10 according to an example of the present invention. Thecommunication system 10 is briefly composed of a network and a pluralityof clients. In FIG. 1, the network and the clients are simply utilizedfor illustrating the structure of the communication system 10.Practically, the network can be an E-UTRAN (evolved-UTRAN) comprising aplurality of evolved Node-Bs (eNBs) and relays in a long termevolution-advanced (LTE-A) system or an access point (AP) conforming toIEEE 802.11 standard in a wireless communication system, or can be aswitch center of an Asymmetric Digital Subscriber Line (ADSL) in awireline communication system, and is not limited herein. The clientscan be mobile phones, laptops, tablet computers, electronic books andportable computer systems. Besides, the network and the client can beseen as a transmitter or receiver according to transmission direction,e.g., for an uplink (UL), the client is the transmitter and the networkis the receiver, and for a downlink (DL), the network is the transmitterand the client is the receiver.

Please refer to FIG. 2, which is a schematic diagram of a communicationdevice 20 according to an example of the present invention. Thecommunication device 20 can be the client or the network shown in FIG.1, but is not limited herein. The communication device 20 may include aprocessor 200 such as a microprocessor or Application SpecificIntegrated Circuit (ASIC), a storage unit 210 and a communicationinterfacing unit 220. The storage unit 210 may be any data storagedevice that can store a program code 214, accessed and executed by theprocessor 200. Examples of the storage unit 210 include but are notlimited to a subscriber identity module (SIM), read-only memory (ROM),flash memory, random-access memory (RAM), CD-ROM/DVD-ROM, magnetic tape,hard disk and optical data storage device. The communication interfacingunit 220 is preferably a transceiver and is used to transmit and receivesignals according to processing results of the processor 200.

Please refer to FIG. 3, which is a flowchart of a process 30 accordingto an example of the present invention. The process 30 is utilized in areceiver of the communication system 10 shown in FIG. 1, to handle aretransmission of a HARQ scheme. The process 30 may be compiled into theprogram code 214 and includes the following steps:

Step 302: Start.

Step 304: Receive a first payload from a transmitter in thecommunication system.

Step 306: Feedback a resource index to the transmitter, to indicate asize for a second payload in the next reception, when the receiver isunsuccessful to decode the first payload into a plurality of informationbits.

Step 308: End.

A plurality of information bits are encoded into the first payload by acorresponding transmitter by using an error correction code (ECC), andthe first payload is transmitted to the receiver. According to theprocess 30, after receiving the first payload, the receiver decodes thefirst payload into a plurality of decoded bits by using the ECC. Underan assumption that the transmitter also uses an error detection code(EDC) to encode the plurality of information bits, the receiver cancheck whether the plurality of decoded bits are correct, i.e., the sameas the plurality of information bits. If there is an error in theplurality of decoded bits, the receiver feedbacks the resource indexwhich can be referred to as a negative acknowledgment (NACK) to indicatethe size for the second payload. Then, the transmitter encodes all orpart of the plurality of information bits into the second payloadaccording to the resource index, for the next reception of the receiver.The process 30 continues until the receiver obtains the plurality ofinformation bits.

As a result, the transmitter adaptively adjusts the size of a payload tobe retransmitted according to a requirement of the receiver, andresources can be used efficiently in the HARQ scheme. Please note that,the resource index is used to indicate the transmitter to adjust thesize of the payload to be retransmitted according to the requirement ofthe receiver, and methods of generating the resource index and contentsincluded in the resource index are not limited herein. For example, thereceiver can generate the resource index by using damage informationwhich is related to information (e.g. severity and/or amount) of theerror in the plurality of decoded bits, and such damage information isgenerated when decoding the first payload or jointly decoding the firstpayload and successive retransmitted payloads. Alternatively, thereceiver can combine the damage information and quality information ofthe channel between the transmitter and the receiver to generate theresource index.

For further illustrating the present invention, please refer to FIG. 4,which is a schematic diagram of a transmitter and receiver communicatingwith each other according to an example of the present invention. Thetransmitter TX and the receiver RX can be realized in the communicationdevice 20 shown in FIG. 2. The transmitter TX and the receiver RXoperate according to the process 30. A payload PLD with a size SZ isfirst transmitted by the transmitter TX to the receiver RX. PayloadsPLD_1-PLD_n are successive retransmissions for the payload PLD, when thepayload PLD is not decoded successfully by the receiver RX. In thissituation, the receiver feedbacks resource indices IND_1-IND_n to thetransmitter TX to indicate sizes SZ_1-SZ_n for the payloads PLD_1-PLD_n,respectively.

In detail, the transmitter TX uses an ECC and an EDC to encodeinformation bits into the payload PLD. Then, the transmitter TXtransmits the payload PLD to the receiver RX. After receiving thepayload PLD, the receiver RX decodes the payload PLD into decoded bits,and the EDC is used to check the correctness of the decoded bits. If thedecoded bits are correct, the receiver feedbacks an ACK to inform thetransmitter TX to transmit another new payload, and a retransmission isnot needed. Otherwise, the receiver RX extracts damage informationgenerated during decoding, and uses the damage information to generatethe resource index IND_1. Alternatively, the receiver RX combines thedamage information and quality information of a channel between thetransmitter TX and the receiver RX to generate the resource index IND_1.The receiver RX feedbacks the resource index IND_1 to the transmitter TXto indicate the size SZ_1 for the retransmission of the payload PLD_1.

Please note that, the ECC can be a turbo code, a low-densityparity-check (LDPC) code, a convolutional code or any code providingforward error correction, and is not limited herein. The EDC is used tocheck if there is an error in the decoded bits, and is preferably a CRC.The damage information can be any information (e.g. severity and/oramount) of the error of the decoded bits, and is not limited herein.Preferably, the damage information can be a function of soft outputvalues generated by the receiver RX when decoding the payload PLD. Thesoft output values, such as log likelihood ratios (LLRs), are byproductswhen the receiver RX uses an iterative decoding of at least oneiteration to decode the payload PLD. Therefore, it does not need toobtain the damage information by additional computations. Besides, sincethe soft output values are generated in each iteration, the receiver RXcan adopt all or part of the soft output values as contributed softoutput values for the function. For example, only the soft output valuesat the last iteration are adopted as the contributed soft output values,since those are the most reliable soft out values comparing to the softoutput values generated in previous iterations.

On the other hand, the function can be any transformation method capableof transforming the contributed soft output values into the damageinformation that can represent the severity of the error of the decodedbits, and is not limited herein. For example, the function outputs apercentile of a cumulative distribution function (CDF) of thecontributed soft output values. The percentile can be an nth percentilebelow which is n % of the contributed soft output values. Therefore, thelower the percentile is, the more the severity of the error of decodedbits is. A value of the n % can be 5%, 10%, 20%, etc., and is notlimited herein. Another example of the function is an average of aplurality of the contributed soft output values. Preferably, theplurality of the contributed soft output values can be the contributedsoft output values lower than a percentile of the CDF of the pluralityof the contributed soft output values. In other words, only thecontributed soft output values lower than the percentile are averaged toobtain the damage information. Furthermore, since range of the damageinformation is wide and arbitrary, a lookup table including only afinite number of values can be used to limit the range of the damageinformation. More specifically, instead of using an output of thefunction as the damage information, the output of the function is mappedto one of the finite number of values in the lookup table. The one ofthe finite number of values is then used as the damage information toreduce complexity required for successive processing of the damageinformation. The lookup table is established by using a plurality ofnumerical experiments, and is preferably stored in the receiver RX.Therefore, the above illustration can be summarized into FIG. 5, whichis a flowchart 50 for generating the damage information according to anexample of the present invention.

Besides, the quality information of the channel between the transmitterTX and the receiver RX can be estimated by the receiver RX, or isobtained from another component of the communication device 20. As aresult, the receiver RX can generate the resource index IND_1 by usingthe damage information and the quality information of the channelbetween the transmitter TX and the receiver RX.

After the transmitter TX receives the resource index IND_1 indicatingthe size SZ_1 for the payload PLD_1, the transmitter TX encodes part orall of the information bits into the payload PLD_1. In detail, thetransmitter TX selects a combination of a coding rate of the ECC, apuncturing rule, a modulation format and a resource block allocationaccording to the resource index IND_1, to generate the payload PLD_1with the size SZ_1, and transmits the payload PLD_1 to the receiver RX.An example of adjusting the coding rate simply is that increasing thecoding rate if the resource index IND_1 is above a predefined threshold,otherwise reducing the coding rate.

After receiving the payload PLD_1, the receiver RX combines the payloadsPLD and PLD_1 to perform a joint decoding. If the decoded bits arecorrect, the receiver RX feedbacks the ACK to inform the transmitter TXto transmit another new payload. Otherwise, the resource index IND_2 isgenerated according to the above illustration and is fed back toindicate the size SZ_2 for the retransmission of the payload PLD_2. Ifthe information bits cannot be obtained by the receiver RX afterperforming the joint decoding of the payloads PLD, PLD_1 and PLD_2, thereceiver RX continues feeding back the resource indices IND_3-IND_n toindicate retransmissions of the payloads PLD_3-PLD_n until theinformation bits are obtained by the receiver RX. When moreretransmitted payloads are received and jointly decoded, there is ahigher probability for the receiver RX to obtain the information bits.

In short, if the damage information implies that the receiver RX mayonly need a few more information (e.g. redundant bits and/or moreinformation bits) to obtain the information bits, the receiver RXgenerates the resource index to indicate the transmitter TX to reduce asize of a payload to be retransmitted, and the transmitter TX transmitsthe payload with fewer resources. Oppositely, if the damage informationimplies that the receiver RX may need much more information to obtainthe information bits, the receiver RX generates the resource index toindicate the transmitter TX to increase the size of the payload to beretransmitted, and the transmitter TX transmits the payload with moreresources. In either way, the transmitter TX transmits the payload withenough information for a successful decoding according to the resourceindex, the receiver RX can obtain the information bits with just oneretransmission or a few retransmissions. In this situation, not only theresources are preserved, but a delay caused by the HARQ scheme isreduced due to the one or a few retransmissions.

In comparison, a receiver according to the prior art receives eachpayload with a fixed size in each retransmission. The resources used areexcessive when only a little more information is needed by the receiver,and are insufficient when the much more information are needed by thereceiver. Not only the resources are wasted, but the delay caused by theHARQ scheme is increased due to more retransmissions. Therefore,throughput of the communication system is decreased.

The abovementioned steps of the processes including suggested steps canbe realized by means that could be a hardware, a firmware known as acombination of a hardware device and computer instructions and data thatreside as read-only software on the hardware device or an electronicsystem. Examples of hardware can include analog, digital and mixedcircuits known as microcircuit, microchip, or silicon chip. Examples ofthe electronic system can include a system on chip (SOC), system inpackage (SiP), a computer on module (COM) and the communication device20.

In conclusion, the present invention provides a method for handling aHARQ scheme in a communication system. When a receiver requests aretransmission of a payload, a transmitter adaptively adjusts a size ofthe payload according to an indication from the receiver. The indicationrelates to amount of information required by the receiver to decode thepayload successfully, and is generated by using damage information andpossibly quality information of a channel between the transmitter andthe receiver. The method not only preserves resources required for theretransmission, but only a few retransmissions are required by thereceiver to decode the payload successfully. Therefore, not onlythroughput of the communication system is increased, but a delay causedby the HARQ scheme is reduced due to the few retransmissions.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A method of handling a retransmission of a hybridautomatic repeat request (HARQ) scheme for a receiver in a communicationsystem, the method comprising: receiving a first payload from atransmitter in the communication system; generating a resource index byusing damage information of the first payload and quality information ofa channel between the transmitter and the receiver; and feeding back theresource index to the transmitter, to indicate a size for a secondpayload in the next reception, when the receiver is unsuccessful todecode the first payload into a plurality of information bits; whereinthe transmitter encodes the plurality of information bits into the firstpayload by using an error correction code (ECC); wherein the damageinformation is a function of a first plurality of soft output values ofthe first payload generated by the receiver when decoding the firstpayload, and the first plurality of soft output values of the firstpayload are part of soft output values generated by the receiver whendecoding the first payload, and the part of the soft output values aregenerated by the receiver at the last iteration when a iterativedecoding is used to decode the first payload.
 2. The method of claim 1,wherein the damage information is a percentile of a cumulativedistribution function (CDF) of the first plurality of soft output valuesof the first payload.
 3. The method of claim 1, wherein the damageinformation is an average of a second plurality of soft output values ofthe first payload, wherein the second plurality of soft output values ofthe first payload are soft output values lower than a percentile of theCDF of the first plurality of soft output values of the first payload.4. The method of claim 1 further comprising: mapping the damageinformation into one of a plurality of discrete values by using a lookuptable.
 5. The method of claim 4, wherein the lookup table is establishedby using a plurality of numerical experiments.
 6. The method of claim 1,wherein the quality information of the channel between the transmitterand the receiver is obtained or estimated by the receiver.
 7. The methodof claim 1, wherein the ECC is a turbo code, a low-density parity-check(LDPC) code or a convolutional code.